Dual Mach-Zehnder distributed optical fiber disturbance sensing system adopts optical wave to achieve intrusion detection and position, has the advantages of long-distance monitoring, high-precision positioning, low energy dependence, high environmental tolerance, anti-electromagnetic interference, corrosion resistance, etc. Recently, Shangran Xie, et, al. (Positioning error prediction theory for dual Mach-Zehnder interferometric vibration sensor, Journal of Lightwave Technology, 2011, 29:362-368) analyzes the influence of various noise on the positioning accuracy, and predicts the positioning accuracy of the system under different SNR (short for Signal to Noise Ratio); the article of Qinnan Chen, et, al. (An Elimination Method of Polarization-Induced Phase Shift and Fading in Dual Mach-Zehnder interferometry Disturbance Sensing System, Journal of Lightwave Technology, 2013, 31:3135-3141) discloses an elimination method of compensating the polarized noise in the system thus improving the positioning accuracy. The article of Xiangdong Huang, et, al. (Configurable Filter-Based Endpoint Detection in DMZI Vibration System, Photoics Technology Letters, 2014, 26:1956-1959) adopts full-phase filter to accurately position the disturbance start point.
Currently, the positioning accuracy of dual Mach-Zehnder distributed optical fiber disturbance sensing system can fall within the range of 20 m (sampling rate 10 MS/s, theoretical precision is 10 m) when sensing distance is short. However, due to the limitation of optical structure of the system, backscatter noise of the optical fiber has more and more obvious influence on SNR with the increase of sensing distance, which seriously affects the system positioning accuracy and restricts the system sensing distance.